<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        function A() {
  console.log("A is running")
}

function B(callback) {
  console.log("B Start")
  callback() // A is running
  console.log("B End")
}

B(A)

    </script>
</body>
</html>